The present invention relates to video compression, and more particularly to accurately detecting a blockiness period induced by DCT-based codecs.
Companies that distribute video over compressed pathways, such as satellite or digital cable distributors, have hundreds of channels which they need to monitor for defects. Many companies choose to use equipment using single ended measurement algorithms, such as that described in U.S. patent application Ser. No. 09/152,495 entitled xe2x80x9cPicture Quality Measurement Using Blockinessxe2x80x9d and filed Sep. 10, 1998, for realtime measurements. However these single ended blockiness measurements do not decide whether the blockiness being detected is caused by unacceptable codec (COder/DECoder) deformation of the image, or whether the blockiness is the natural result of blockiness that exists within the image, most commonly introduced by lettered graphics imposed on the image.
This task is complicated by the fact that changes to the codec, or digital pathway, may change the periodicity on the fly. A video stream also may be subject to more than one codec before the end viewer sees it, and so may have more than one periodicity in the picture.
Therefore what is desired is an accurate blockiness period detection algorithm for DCT-based codecs to decide whether blockiness that exceeds specified thresholds is caused by the codecs or natural events in the image.
Accordingly the present invention provides an accurate blockiness period detection of DCT-based codecs using a histogram-based technique. Each image in an input video signal is processed to determine a blockiness period having a maximum correlation value. The blockiness period so identified is accumulated in a histogram. The maximum peak in the histogram corresponds to the blockiness period induced by the DCT-based codecs. Identified blockiness periods from the image may be compared with those of immediately preceding images from the video signal so that only if there is essentially equivalence is the histogram incremented for that blockiness period. Likewise if a blockiness period does not have a maximum for a given number of images or time intervals, that period is deleted from the histogram. Further if one of the peaks exceeds the peak associated with the codec blockiness period by a specified factor, then the codec blockiness period is deemed to have changed and is then associated with the new maximum peak.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.